Nowadays, the Dendrobium species is considered to be the most precious Chinese herb for treating ophthalmic defects. A Dendrobium species belongs to an orchid family, and its steam is the mainly medicinal part. It tastes a little sweet and brackish. Some Chinese medical codices disclose that the Dendrobium species is the curative for some illnesses such as salivary defects, stomach defects, and ophthalmic defects. According to our previous research experience, it appears that the Dendrobii Caulis is the most medicinal species.
A retinal pigment epithelium (RPE) is a monolayer cell at the surface layer of the retina, which is located between the Bruch's membrane and the photoreceptors. The villous processes at the top of RPE are connected to the outer segments of the photoreceptors, and the basal inflodings at the bottom of RPE are connected to the choroids via the Bruch' membrane. Since the RPE can effectively remove or transmit the toxic materials and the metabolite of the choroid coat and the retina, it performs a very important blood-retinal barrier. In addition, the RPE has many functions, such as receiving light, phagocytizing the outer segments separated from the rod cell and the cone cell because of light stimulation, catabolizing the phagosome, synthesizing the extracellular matrix and the melanin, detoxifying the medicine, providing the essential material for reproducing the outer segments of the photoreceptor, storing and transmitting the Vitamin A, synthesizing the rhodospin, and forming the adherent force of the retina. According to the statistics, a RPE of rat can remove 25000 outer segments separated from the rod cells and the cone cells because of light stimulation in one day, which obviously shows the importance of the frequent phagocytic metabolism (Mayerson and Hall, 1986). The normal phagocytosis of the RPE plays a critical role in maintaining the health of the photoreceiptors in the retina. Once the function of phagocytosis is reduced, it will result in the degeneration of the photoreceptors. Although the RPE will be dead or moved to someplace else with the increasing age, the aged RPE still owns the phagocytic ability. However, the digestion ability of the RPE is obviously reduced (Boulton and Marshall, 1986). It appears that the numbers of the human photoreceptors will be decreased per year with a rate ranged from 0.2 to 0.4% per year (Panda-Jonas et al., 1995). Further, the lost quantity of the rod cells are more than those of the cone cells, which causes the diseases and the vision degradation of the aged people. Therefore, maintaining the RPE function is quite important for the visional system.
Although a nitric oxide (NO) is a small, unstable gas molecule with a half-life of several seconds, it has various kinds of physiological functions. Since the NO is an electrically neutral gas, it can arbitrarily penetrate the cell wall. On the other hand, since the NO has the unpaired electron, the NO molecule is highly reactive as the free radicals so that it will penetrate the cell membrane and react immediately after being formed. In the immune system, the NO plays a defensive role and is toxic to cells. In the blood vessel system, the NO is a so-called endothelium derived relaxing factor (EDRF). And, in the central nervous system, the NO acts as a neurotransmitter.
The NO is released from the process of transferring L-arginine into L-citrulline via a nitric oxide synthase (NOS). However, the detailed transferring mechanism of how to release the NO is still unclear till now. The NOS includes three kinds of isoforms, a neuronal NOS, an endothelial NOS and an immunologic NOS. The neuronal NOS and the endothelial NOS are constitutive forms, named as cNOS, whose activities are regulated by the calcium ion (Ca++) and the calmodulin, and the concentration of the released NO is in the level of nano-molarity (nM). The immunologic NOS is an inducible form, named as iNOS, whose activity is not regulated by the Ca++ and the calmodulin, and the concentration of the released NO is in the level of milli-molarity (mM). The genes of the cNOS and the iNOS are respectively located on different chromosomes. Taking human beings as an example, the neuronal NOS is located on the chromosome 12, the endothelial NOS is located on the chromosome 7, and the immunologic NOS is located on the chromosome 17 (Goldstein et al., 1996).
In retina, the NOS has been found in the retinal neuron, RPE, amacrine cells, ganglion cells, and Muller cells. It appears that the NO plays an important role in the physiology and pathology, and is closely related to the functions of the eye.
Because the NO can regulate the voltage-gated ion channel on the photoreceptors, it is conjectured that the NO is related to the transmission of the light messages. It's found that the NO owns the ability of regulating the blood flow of the retina under a basal condition or an ischemia environment (Tilton et al., 1993). Further, it's believed that the NO may own the ability of regulating the damage degrees of the blood vessels in the retina, in which the damage is caused by diabetes (Goureau et al., 1994). In addition, when the retinal glial cells and the RPE are stimulated by the LPS, IFN-g, and the TNF-a, the NOS will be largely expressed, which largely increase the production of the NO. In other words, under the conditions that the retina is inflamed or infected, the NO might play a role in the defense and protection mechanisms.
Till now, the position and the characteristics of the cNOS in the photoreceptor are still unclear. Some references disclose that the main body of the photoreceptor has the cNOS activities, and other references disclose that only the photoreceptor outer segments own the cNOS activities. The released NO can regulate the transmission of light, the transmitted message of the neutron synapase, and the blood flow of the retina under a physiological condition or an ischemia environment. The iNOS activity can also be found in some cells in the retina, such as the RPE and the Muller cells. In the culture of a bovine RPE, after being stimulated for 12 hours with the IFN-γ, LPS, and TNF-α, a mass of NO will be released for at least 96 hours. The effects of the cytokines on the RPE iNOS activity are quite complex. In a bovine RPE, for instance, being stimulated by the LPS and the IFN-γ, or the IFN-α are necessary for releasing a mass of NO. The bFGF inhibits the functions of NOS, but the TGF-β slightly enhances the functions of the NOS. For a human RPE, it is necessary to be stimulated by the Interleukin-1 β to release a mass of NO. However, the LPS is not the necessary factor to stimulate a human RPE. In addition, the TGF-β obviously inhibits the release of the NO in a human RPE.
When infected by bacteria, the expressions of iNOS may be beneficial because the released NO will kill the invaded microorganism. Contrarily, in some cases, when the released NO is exceeded, the released NO will result in the autoimmune diseases or the septic shock. In 1994, the first evidence for explaining the relationship between NO and the inflammation of the fundus oculi is proposed, and the reference also proposed that the uveitis resulted from the endotoxins can be blocked by the iNOS inhibitor. On the other hand, it appears that the aFGF and the bFGF can inhibit RPE from generating a mass of NO by treating the RPE with IFN-γ and LPS. Since it is the expression of the iNOS, but not the stabilities of the iNOS being mRNA, is inhibited, it's conjectured that the FGF will protect the RPE from being damaged by the endotoxins and the cytokines. Thus, it can be seen that the iNOS also plays a role in regulating the immunity of the retina.
The common retinal diseases include the proliferative diabetic retinopathy caused by the diabetes, the proliferative vitreoretinopathy, and the Aged-macular degeneration. However, the retinal diseases are the hardest diseases to cure in the ophthalmic defects. The hyperglycemia accelerates the glycation, which forms the advanced glycation end products (AGEs), and it is believed that the AGES closely relates to the vascular complication or the neuronal complication (Lu et al., 1998). An unstable schiff base is formed via the nonenzymatic reaction between the aldehyde group or the ketone group of the reducing sugar and the primary amino acids of the protein. Then, an amadori product is formed from the schiff base via the amadori rearrangement (Munch et al., 1997). And, the advanced glycosylation end product (AGE) will be formed from the amadori product via the rearrangement process. It is known that the nonenzymatic glycosylation is not a reversible reaction and usually occurs at the protein having a long half-life. While the AGE formation results in cross-linking, the protein molecule would have a resistance to the protease. Therefore, the accumulation of the AGE would be an aging mark (Handa et al., 1999). With the increasing age, the AGE amounts in the pyramidal neurons of the brain, the Bruch's membrane and the collagen will increase gradually. The reactive rate of the nonenzymatic glycosylation is a primary reaction, and the reaction rate is dependent on the concentrations of the reducing sugar and the protein. Usually, a diabetic patient has a higher blood glucose concentration than normal people, so that the glycosylation situation will be increased. It is known that the diabetic patients have higher probabilities of having some diseases or symptoms for the normal people are all directly related to the AGE, in which the disease or symptoms include the atherosclerosis, the kidney impair, the vessel damage, the neuron disease, the retinopathy, and the apoplexy (Zimmerman et al., 1995). The main reason for the aggregation of the erythrocyte, resulted from the diabetes, is that the tertiary structure of the albumin is changed after being glycosylated, so that the glycosylated albumin loses the functions of the anti-aggregation. Further, the reason for changing the permeability of the glomerulus is the glycosylation of the albumin but not the glycosylation of the glomerular basement membrane. In addition, the glycosylated protein has a better ability for penetrating the blood brain barrier.
The AGE can combine with some receptors on the cell surface or some proteins. The known receptors include the scavenger receptors type I, the scavenger receptors type II, the receptor for AGE (RAGE), OST-48 (AGE-R1), 80K-H phosphoprotein (AGE-R2), and the galectin-3 (AGE-R3). Besides, the RAGE can be found at the surfaces of the monocyte, the macrophage, the endothelial cell, and the glia cell. When the cell is activated by the AGE, the expressions of the extracellular matrix protein, the vascular adhesion molecules, and the growth factors will increase. Depending on the different cell types and the transmitted signals, some phenomena will occur accompanied with the above situation, such as the chemotaxis, the angiogenesis, the oxidative stress, the cell proliferation and the programmed cell death. It appears that the various cells in the human brain are able to express different RAGEs, which remove the AGE. When the remove ability is lost, the AGE will be accumulated outside the cell, which induces the inflammation reaction of the central nervous system. Furthermore, the AGE will induce the expressions of both the retinal vascular endothelial growth factor of the RPE and the PDGF-β (Handa et al., 1998). The AGE plays an important role in the aging process, so that designing a pathological model by the glycosylated albumin for developing a new medicine is very important.
The most important growth factor in the liver is the hepatocyte growth factor/scatter factor (HGF/SF), which is formed by combining the 60 KDa heavy chain (a chain) with the 30 KDa light chain (β chain) through the disulfide bond. The newly formed HGF/SF is the prepro HGF/SF, which needs to be modified by an enzyme for forming the heterodimeteric form before having a biological activity. The HGF is a multi-function growth factor, which not only has the ability for regulating the growth of the various cells, but also plays an important role in the tissue repair and the organ regeneration. The internal distribution of the HGF is very extensive, wherein the liver has the highest quantity of the HGF. Furthermore, the HGF can be found in the pancreas, the thymus, the blood, the small intestines, the placenta and so forth. In addition, the HGF/SF or the HGF/SF receptors are found in the eye secretions and the eye tissues, such as the tears, the lachrymal gland, and the cornea, so that it is conjectured that the HGF may play a role in the regulation of eyes (Li et al., 1996). Besides, it's known that the RPE has both the HGF and the HGF receptor (c-Met). Since the tyrosine phosphorylation of the c-Met expresses all the time, the HGF may be a growth factor with the self-stimulation function for the RPE. Further, the HGF may be related to the development of the retina (Sun et al., 1999), the wound healing, and the newborn retinal vessels (He et al., 1985).
From the above, it is known that RPE plays an important role in retinal regulation mechanisms. Meanwhile, we have found and proved that the Chinese herb, Dendrobium species, is able to enhance or inhibit some functions or regulation mechanisms in RPE. More specifically, the Dendrobium species can enhance the expressions of RPE phagocytosis, the NO formation of the RPE, the gene expressions of the RPE liver hepatocyte growth factor. The Dendrobium species can inhibit the gene expressions of the bFGF, the VEGF and the TGF-β in the RPE under a normal condition and an ischemia environment. Consequently, the relevant researches about the enhancing factors of the RPE activities are important for improving the health of the body. That is to say, the relevant research is absolutely worthy in the relevant industries.
Because of the technical defects described above, the applicant keeps on carving unflaggingly to develop “EXTRACT OF PLANT DENDROBII CAULIS AND PREPARING PROCESS THEREOF” through wholehearted experience and research.